Modem Oil Patch applications now require alloys of increasing corrosion resistance and strength. These increasing demands arise from factors including: deep wells that involve higher temperatures and pressures; enhanced recovery methods such as steam or carbon dioxide (CO.sub.2) injection; increased tube stresses especially offshore; and corrosive well containments including: hydrogen sulfide (H.sub.2 S), CO.sub.2, and chlorides.
Materials selection is especially critical for sour gas wells--those containing H.sub.2 S. Sour wells' environments are highly toxic and extremely corrosive to traditional carbon steel oil and gas alloys. In some sour environments, corrosion can be controlled by using inhibitors along with carbon steel tubulars. The inhibitors however, involve continuing high cost and are often unreliable at high temperatures. Adding corrosion allowance to the tubing wall increases weight and reduces interior tube dimensions. In many cases, the preferred alternative in terms of life-cycle economy and safety is the use of a corrosion resistant alloy for tubulars and other well components. These corrosion resistant alloys eliminate inhibitors, lower weight, improve safety, eliminate or minimize workovers and reduce downtime.
Martensitic stainless steels, such as the super 13% chromium alloys satisfy corrosion resistance and strength requirements slightly corrosive oil patent applications. (This specification describes all compositions in weight percent, unless specifically expressed otherwise.) The super 13% alloys however lack the moderate corrosion resistance and strength required of low-level-sour gas wells. Cayard et al., in "Serviceability of 13Cr Tubulars in Oil and Gas Production Environments," published sulfide stress corrosion data that indicate 13Cr alloys have insufficient corrosion resistance for wells that operate in the transition region between sour gas and non-sour gas environments.
Austenitic-high-nickel alloys such as alloys 825, 925, G-3 and C-276 provide alloys with increasing levels resistance to corrosive-sour gas environments. These nickel-base alloys provide the combination of strength and corrosion resistance necessary to act in L. the most demanding Oil Patch applications. Unfortunately, these alloys are often too expensive for low-level-sour gas applications.
It is an object of this invention to provide an alloy with sufficient corrosion resistance to function in low-level-sour gas environments.
It is a further object of this invention to provide an alloy with sufficient mechanical strength to serve in demanding oil and gas tubing applications.
It is a further object of this invention to provide a low-nickel alloy with sufficient strength and corrosion resistance to serve in low-level-sour gas environments.